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What Forms of Life Could We Find on Other Planets?
Answer from Ken Natco, techno geek and student of quantum mechanics:
For a number of reasons, any life forms would likely be carbon based because the carbon atom is so well suited to forming a vast number of organic compounds. Silicon and germanium have been suggested as alternatives because they occupy the same group in the periodic table as carbon, but their compounds are less stable. All life on Earth is carbon based and uses water as a solvent. Methane could possibly be used by alien life forms, though without evidence, this is pure speculation.
There are earth life forms that make use of silicon. Diatoms have silicates in their skeletons. Like these:
There is even a theory that life on Earth had silicate minerals to thank for getting started, giving a little credibility to the implication in Genesis that man was formed from clay. Silicon is far more abundant on the Earth than carbon, but life here uses carbon, not silicon.
Currently our best chance at finding extraterrestrial life is on Mars with the recent discovery of flowing water there, salty as it may be. With its past history of oceans and a denser atmosphere, life might have developed there, and once life gets a foothold it can be very tenacious. There are some life forms on Earth in places one would not think possible. For instance, here are some worms that live by thermal vents in the bottom of the ocean:
Then there are the bizarre creatures called water bears (tardigrades) that can survive for years without water and can withstand extreme radiation that would destroy any other form of life. They can survive extreme cold and the vacuum of space. Add water and they continue to live! They truly look quite alien, but they are everywhere, even in your backyard:
The existence of creatures like this lends credibility to the thought that life may exist in environments that we would find quite inhospitable.
What we have traditionally thought of as the "Goldilocks zone" for life has been reconsidered. The discovery of subsurface oceans on Titan, Europa, and Enceladus has given rise to speculation that they may harbor life. Their heat sources are the moons' cores and the tidal forces exerted by their parent planets, Jupiter or Saturn. Actually finding any life there, if it exists, will be extremely difficult for obvious reasons.
The next-best method of finding evidence of extraterrestrial life may be by spectral analysis of a distant planet's atmosphere. If we found a planet with an oxygen-rich atmosphere, that would be a strong indicator of possible life. The Earth's oxygen was formed by life processes. Elemental oxygen was toxic to the original life that began on Earth. It was the waste product of the original life. It is now a vital part of our biosphere and the ozone layer would not exist without it. The blocking effects it has on ultraviolet radiation enables life as we know it to survive on the surface. Current technology isn't good enough to determine the atmospheric composition of earth-like planets, but the day we discover an earth-type atmosphere will be widely heralded.
The phrase "life as we know it" is important to us. It is the kind of life that would be truly exciting to find. It is the life we would best know how to look for. Life "as we know it" can be extremely strange. We know life develops to be extremely well suited to survive in its particular ecological niche, so we would expect a lot of variation in form. Differences in gravity would result in different physical adaptations. Climate, terrain, length of day, atmospheric pressure--all are variables that would produce different adaptations. Cosmic accidents also play an extremely important role in life's development. If the asteroid that caused the dinosaurs to go extinct had missed the Earth, what would life be like today? Would higher intelligence have ever developed? Life changes to adapt to its environment. Extreme changes, like ice ages, force adaptation.
Intelligence is an adaptation that enables us to deal very creatively with our environment. In a very stable environment, there would be little pressure for intelligent life to arise. We might find a seemingly perfect planet for life, but it might be too perfect. Without a tilt to its axis, it would have no seasons. With no moon, it would have no tides. The ideal place to expect intelligent life would be a world with a rather tumultuous history, but not too tumultuous. There is another kind of Goldilocks zone that is a little harder to define, but just as essential as liquid water, magnetic field to shield from radiation, oxygen, livable temperatures, and a stable orbit: the right amount of change. Too much, and life is destroyed. Not enough, and things remain static.
I believe this is especially true for the development of intelligent life. For this reason, I don't assume that there are necessarily a lot of alien civilizations that are much more advanced than humans. What will it take for us to become more intelligent than we are now? It is likely not to be a pleasant experience. We do face many predictable challenges to our survival--war, pollution, and resource depletion, not to mention global warming. As we seek life elsewhere in the universe, let us be cognizant of our own fragility. If we do clear the hurdles we face, we may yet have the opportunity to learn firsthand what life in the universe really is like, instead of just speculating about it.
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